Study on grouting reinforcement mechanism and experiments in fractured rock mass for underground engineering

Grouting is considered an effective reinforcement method for fractured rock masses in underground engineering. Although the traditional grouting technology mainly plays a bonding role, it has a limited effect on the reinforcement of the surrounding rock fractures. In order to improve the density of the slurry and enhance its reinforcement effect, an expansion agent can be mixed in the grouting material. Based on the Mohr–Coulomb criterion, an equivalent model for slurry reinforcement of fissured rock masses was established in this study, with the expressions for rock mass strength under various reinforcement techniques derived, and the strengthening mechanism of slurry reinforcement on fissured rock masses elucidated. Through indoor uniaxial compression tests and numerical simulation methods, this study investigates the crack initiation and propagation characteristics of rock masses with different fracture angles, and analyzes the reinforcement mechanisms and effects of ordinary slurries and expansion slurries on fractured rock masses. The study indicates that expansion slurry provides superior reinforcement compared to ordinary slurry, with the increase in expansion stress significantly improving the grouting reinforcement effect. Grouting improves the strength of fractured rock masses, though it does not fully restore their original strength. Post-grouting, the fissured rock mass exhibits a change in damage mode, with initial crack propagation occurring along the slurry–rock interface. Subsequently, the cracks propagate obliquely toward the prefabricated fissures, culminating in the overall splitting failure of the rock mass with the slurry-rock interface as the core. Through the expansion agent grouting reinforcement method, the transportation roadway of Jintong Coal Mine was reinforced, and the surrounding rock was effectively controlled, which proved the superiority of expansion agent grouting reinforcement.